Preliminary studies in this laboratory indicate that a highly photoreactive, common dietary substance, tetraiodofluorescein (TIF, FDA-approved red dye #3), may be a potent photocataractogenic agent. We have demonstrated that TIF: (1) crosses the blood-aqueous barrier and enters the anterior chamber; (2) can produce a host of singlet oxygen-mediated effects on soluble proteins as well as on membrane-associated proteins and lipids; these effects include the photooxidation of key aromatic amino acids, a photochemical, non-disulfide, covalent, intra- and inter-crosslinking of soluble and membrane proteins, and the generation of membrane lipid hydroperoxides; (3) is a potent, irreversible, photoinhibitor of the lens epithelial Na-pump; and (4) can generate lenticular opacification in mice via short term exposure to low intensity visible radiation (greater than 450 nm), probably through a combined interference with lens carrier-mediated Na-transport and the generation of photocrosslinked protein aggregates. Unfortunately, none of the numerous animal feeding studies which have led to FDA approval of any natural or synthetic food colorant has taken phototoxicological impacts into consideration. We propose: (1) to examine more carefully in a 180 mouse study whether dietary TIF plays a significant light-mediated cataractogenic role and thus may be photobiologically contraindicated for human consumption; (2) to characterize the photochemical consequence of dietary TIF on select soluble and membrane-associated lens proteins; and (3) to examine other food colorants for photochemical activity and singlet oxygen generation capability and their possible effects on corneal endothelial and lens epithelial and fiber cell proteins. In addition we have found that photooxidized and photopolymerized protein species in TIF-generated opacified lenses (in vivo), in normal lenses TIF-phototreated in vitro, and resulting from TIF-phototreatment of lens soluble and insoluble and model oligomeric proteins stain poorly, if at all, with the typical protein detection reagents. It thus is highly probable that previous analyses of photooxidized and photocrosslinked proteins in aged or cataractous lenses have overlooked a large population of such species; consequently, in addition, we will examine aged and human cataractous lenses for photooxidized and photopolymerized species using novel techniques to guarantee their detection.